The Laboratory Model Test And The Numerical Simulation Of Instability On Loess Slope Induced By Rainfall Infiltration

In recent years,with the acceleration of the construction speed of highways and railways,the engineering geological conditions required for engineering construction are becoming more and more complicated.As the most basic geological environment for human activities,high-filled slopes in the loess area are constantly emerging.Due to the special structural and mechanical properties of loess,heavy rainfall can easily lead to erosion damage or even landslides.Sanmenxia City is located in the west of Henan Province.It is the throat fortress of two province.The mileage of highways in this area is 9343 kilometers.As a necessary place for the transfer of eastern industries and the export of resources in the west,the rapid development of traffic demand makes the rational evaluation and utilization of loess fillers in the region increasingly prominent.Based on this,the laboratory model test of loess slope is carried out which takes the Malan loess in Sanmenxia as the research object.The progressive failure process of slope under rainfall is explored.At the same time,the variation of water distribution in slope under cyclic intermittent rainfall is analyzed by using PLAXIS 2D.On the basis of it,the effects of rainfall duration,soil moisture content and rainfall infiltration depth on slope stability are further discussed.The main conclusions as follows:(1)Study on hydraulic characteristics of unsaturated loess.The soil-water characteristic curves and permeability functions of soils under different compaction degrees are estimated by using the existing test data and the typical V-G model.The influence of water content on soil strength parameters,such as cohesion and internal friction angle is also studied.The research shows that the saturated water content of the soil water characteristic curve of different compaction soils tends to decrease with the increase of the compaction of the sample,while the change of residual water content is exactly the opposite;the soil moisture content has a great influence on the shear strength parameters.The main performance is that as the water content increases,the structural jelly of the loess is decomposed and dissolved.The free water film between the soil particles becomes thicker,the suction is reduced,and the soil is cohesive.Both the force and the internal friction angle tend to decrease linearly with increasing water content.(2)Laboratory model test and instability failure mechanism of rainfall infiltration in loess slope.The indoor simulated rainfall test was carried out by using the self-made model trough and remolded loess slope.By real-time monitoring the deformation of the slope and the distribution of water content,the failure mode of the slope instability was derived.The instability process of loess slope is as follows: rainfall infiltration and runoff erosion?softening and collapsing at the toe of the slope and slowly forming a temporary surface ?increasing of the bulk density and pore water pressure of upper soil?generation of cracks?development of cracks and forming weak layers?increasing of the sliding force and decreasing of the shear strength?failure of slope.(3)Study on the infiltration law of slope under rainfall infiltration.The infiltration process of rainwater is actually a process in which the soil gradually absorbs water from saturation to saturation.The infiltration rate of rainwater during rainfall is dynamic: in the first two rainfall tests,the average infiltration rate of rainwater was about 60%~70%,and the average infiltration rate dropped to 43% by the third rainfall.It will remain at around 30%.At this time,most of the rainwater will flow along the slope and merge into slope runoff,which will result in soil erosion and erosion of the slope.As the soil permeability coefficient changes with the infiltration depth,the rainwater infiltration process will produce obvious hysteresis.The infiltration rate of the wetting front will gradually decrease with the increase of the soil depth;the runoff of the slope will make the infiltration capacity is improved,and the slope surface is in a state of pressure infiltration.The infiltration rate of slope rainwater is about 3 times that of the slope top infiltration rate.(4)The variation of slope saturation and matric suction during rainfall infiltration: under repeated rainfall,soil saturation is positively correlated with rainfall duration,and the wetting line moves down to 3m below the slope with rainfall.Here,a transient saturation zone is formed,and the depth of rainfall influence tends to be stable.The infiltration of rainwater will gradually reduce the suction of the matrix of the slope.During the short pause of rain,the continuous matrix suction of the soil in the deep part of the slope will continue to decrease,but the surface soil will start to absorb due to the evaporation of water increase.And with the extension of the rain stop,the effect is more obvious.(5)Stability analysis of rainfall infiltration on loess slope: numerical simulation was carried out by PLAXIS2 D finite element software,and the variation law of slope stability under the influence of rainfall holding time,slope water field and fracture location was studied.The simulation results show that the safety factor of loess slope is affected by rainfall under rainfall infiltration,and it will decrease significantly with the increase of rainfall duration.There is a clear boundary point for the slope stability coefficient curve.The boundary point is mainly related to the critical water content and the critical infiltration depth of the slope.If the slope exceeds the critical value,the slope will be unstable.The development of slope cracks has a great impact on its stability.The occurrence of fissures provides a fast channel for rainwater infiltration,making the effect of rainfall more effective.The location of the crack is different,and the degree of influence is different.The impact of the slope crack on the slope is more serious.